Sports Bra Sister Size Guide

Let’s talk sports bra sister size.

We come in all shapes and sizes and so to do our sports bras. This combination can make finding the perfect sports bra difficult. Sometimes you just can’t find the right fit, no matter how many times you measure yourself or how hard you try.

Sister Sizes to the rescue! Your usual go to size may not work for a new bra, but don’t despair, that’s what sister sizes are for!

What Are Sister Sizes?

Quite simply sister sizes are alternate sizes to your usual size where the cup volume stays the same even though the cup letters and band numbers change. Did I say it was simple?

In theory, if the cups of the bra feel correct but the band doesn’t fit quite right you can move up or down a band size whilst keeping the cup volume the same to help you find your perfect fit.

Why You Should Know Your Bra Sister Size

Not all sports bras are created equal. Add to this that we all have our own unique body shape and finding a bra that fits every time is no easy task.

If this is you, then remember it’s your bra and not you that is the problem. Knowing your sister size will give you greater success in your search for the perfect fit. Particularly if you are trying a new brand or style for the first time.

How to Find Your Sister Sizes

It’s actually quite simple (haven’t I said that before?). Starting at your regular bra size your ‘big sister’ size is simply up a band size and down a cup size. If you’re a 12D then ‘big sister’ size would be 14C.

Your ‘little sister’ size is the opposite, down a band size and up a cup size. You’re 12D would become a 10DD ‘little sister’ size.

It really is that simple. It’s all in the cup. To maintain the same cup volume the cup sizing gets smaller as the band size increases and vice versa. A 10DD, 12D & 14C all have the same cup volume even though the letters differ.

That’s the magic of the sports bra back / cup relationship.

When You Should Not Wear Sister Sizes?

Are there any occasions where you should not use sister sizes? If you’ve got a bit more up top and you need your sports bras to help keep things up. I would not recommend wearing the ‘big sister’ size, the ‘up a band size’ sister size.

Support comes from the band and there is a risk the band will be too loose and not provide the support you need. To ensure you get the support you need it is more common to go down a sister size rather than up.

The Advantage of Sister Sizes

So, you’ve spent a long time researching and searching for the perfect bra for you. It ticks all your boxes, it’s high impact, racerback, wirefree and looks perfect but it is not available in your size. Don’t despair as it is perfectly OK to check if a sister size is available. Go up one cup size and down one band size. Or down a cup size and up a band size. Try it for yourself, it almost always works!

Any Questions?

Both my band and cup don’t feel right, what do I do?

If the band and cup feel slightly loose, try going down a band size whilst keeping the cup size the same; 12D to 10D. If the band fits well but the cup still isn’t quite right, try going up or down by one cup size; try a 10C or 10DD.

If the band and cup feel slightly tight, try going up a band size whilst keeping the cup size the same; 12D to 14D. If the band fits well but the cup still isn’t quite right, try going up or down by one cup size; try a 14C or 14DD.

How do I know to go up or down a sister size?

Which sister size you select depends on how your band feels and where you fasten it. Your band should fit you comfortably on its loosest hook and eye setting.

If you’re on the tightest fastening and it still feels loose, try going down a sister size. If you’re on the loosest fastening and it feels too tight, try going up a sister size.

My sister size still doesn’t fit should I go up or down another size?

I recommend only going up or down one sister size. If the sister size still isn’t the right fit, I recommend doing a remeasure and visiting our fitting room to double check if you started with your right size. If you want further advice, please contact me I am happy to help you.

So, there you have it. A comprehensive sports bra sister size guide giving you everything you need to know to find your sister sizes and your perfect sports bra!

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Determine Your Size With Our Bra Size Calculator

1. Underbust Size

2. Overbust Size

Measuring Your Underbust

Stand straight with your arms hanging casually by your side; if you can get a friend to measure you around your chest, directly under your bust.

Ideally, measure yourself while you are wearing a good fitting bra.  The tape should sit directly under your breasts (where your bra band would normally sit), should be horizontal all the way around and be as tight as possible without being uncomfortable (exactly like your bra’s underband).  This measurement is your Underbust.


Measuring Your Overbust

Still standing straight measure horizontally around the fullest part of your bust (usually over the nipples).  This is best done while you’re wearing a good fitting bra.  The tape should not be to tight resting lightly on your body. Make sure the tape is straight across your back and is parallel to the floor.  This measurement is your Overbust.

Finding Your Perfect Fit

Finding your correct Australian Bra Size is as easy as 1, 2, 3. One; follow the instructions below to find your underbust and overbust size. Two; slide the bars to your correct size position to discover your recommended size. Three; start shopping!

  1. Underbust Size; measure around your chest, directly below your bust. Read more below.
  2. Overbust size; measure around the fullest part of your breasts. Read more below.

Crop Tops

Crop tops can fit differently to cupped bras.  Generally speaking they are more similar to women’s clothing sizes.

XS = 8    S = 10   M = 12   L = 14   XL = 16    XXL = 18

Sports Bras Direct recommends crop tops for cup sizes A-D only. You must also check the specific style of crop top suits the level of impact you require.  Breasts that are bigger than a D cup require more specific support from a cup size sports bra.

Each Brand has a slight variation in their actual measurement guidelines for crop tops. Please check brand specific sizing below to establish the best size crop to suit you.

If you are still unsure on your size we would love to help you, please contact us to arrange your personal fitting appointment.

Brand Specific Size Guides